Ubiquinol

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Ubiquinol
Ubiquinol structure.png
Identifiers
PubChem 9962735
Properties
Molecular formula C59H92O4
Molar mass 865.36 g mol−1
Appearance off-white powder
Melting point 45.6 C
Solubility in water practically insoluble in water
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Ubiquinol is an electron-rich (reduced) form of coenzyme Q10.

The natural ubiquinol form of coenzyme Q10 is 2,3-dimethoxy-5-methyl-6-poly prenyl-1,4-benzoquinol, where the polyprenylated side-chain is 9-10 units long in mammals. Coenzyme Q10 (CoQ10) exists in three redox states, fully oxidized (ubiquinone), partially reduced (semiquinone or ubisemiquinone), and fully reduced (ubiquinol). The redox functions of ubiquinol in cellular energy production and antioxidant protection are based on the ability to exchange two electrons in a redox cycle between ubiquinol (reduced) and the ubiquinone (oxidized) form.[1][2]

Characteristics[edit]

Ubiquinol is a lipid-soluble benzoquinol that is found in all cellular systems and in nearly every cell, tissue, and organ in mammals. Ubiquinol is acquired through biosynthesis, supplementation, and, in small amounts, diet. Ubiquinol has an established role as an essential component of the electron transport chain transferring electrons resulting in ATP synthesis. In mammals, ATP production takes place predominantly in mitochondria and to a lesser extent in other organelles such as the Golgi apparatus or endoplasmic reticulum. The mitochondria typically produce nearly 95% of the energy required for cellular growth, development, and healthy metabolism. The antioxidant action of ubiquinol is now considered to be one of the most important functions in cellular systems.

Ubiquinol is the antioxidant form of CoQ10 and is essential for mitochondrial synthesis of energy. It is the only known lipid-soluble antioxidant that is endogenously synthesized, protecting biological membranes against lipid peroxidation as well as regenerating other antioxidants such as Vitamin C and Vitamin E.

Because humans can synthesize ubinquinol, it is not classed as a vitamin.[3]

Bioavailability[edit]

It is well-established that CoQ10 is not well absorbed into the body, as has been published in many peer-reviewed scientific journals.[4] Since the ubiquinol form has two additional hydrogens, it results in the conversion of two ketone groups into hydroxyl groups on the active portion of the molecule. This causes an increase in the polarity of the CoQ10 molecule and may be a significant factor behind the observed enhanced bioavailability of ubiquinol. Taken orally, ubiquinol exhibits greater bioavailability than ubiquinone.[5]

However, there are authorities that dispute whether ubiquinol is more bioavailable in practice rather than in theory compared to CoQ10 supplements because those have their CoQ10 molecules dissolved in lipid micelles, which then deliver their cargo to the plasma membrane in the intestinal wall. There they dissolve via simple diffusion in the intestinal cells, then onto the lymphatic vessels, and then into the venous system. Since ubiquinol and CoQ10 are redox pairs and can and are rapidly inter-converted in the body, it is not clear that ubiqinol's more hydrophilic nature compared to CoQ10 is of practical significance.[6]

Content in foods[edit]

In foods, there are varying amounts of ubiquinol. An analysis of a range of foods found ubiquinol to be present in 66 out of 70 items and accounted for 46% of the total coenzyme Q10 intake. The following chart is a sample of the results.[7]

Food Ubiquinol (μg/g) Ubiquinone (μg/g)
Beef (shoulder) 5.36 25
Beef (liver) 40.1 0.4
Pork (shoulder) 25.4 19.6
Pork (thigh) 2.63 11.2
Chicken (breast) 13.8 3.24
Mackerel 0.52 10.1
Tuna (canned) 14.6 0.29
Yellowtail 20.9 12.5
Broccoli 3.83 3.17
Parsley 5.91 1.57
Orange 0.88 0.14

Molecular aspects[edit]

Ubiquinol is a benzoquinol and is the reduced product of ubiquinone also called coenzyme Q10. Its tail consists of 10 isoprene units.

Ubiquinol

The reduction of ubiquinone to ubiquinol occurs in Complexes I & II in the electron transfer chain. The Q cycle[8] is a process that occurs in cytochrome b,[9][10] a component of Complex III in the electron transport chain, and that converts ubiquinol to ubiquinone in a cyclic fashion. When ubiquinol binds to cytochrome b, the pKa of the phenolic group decreases so that the proton ionizes and the phenoxide anion is formed.

Ubiquinol, semiphenoxide

If the phenoxide oxygen is oxidized, the semiquinone is formed with the unpaired electron being located on the ring.

Ubiquinol

A page on Proteopedia, Complex III of Electron Transport Chain,[11] contains rotatable 3-D structures of Complex III, which may be used to study the peptide structures of Complex III and the mechanism of the Q cycle.

References[edit]

  1. ^ Mellors, A; Tappel, AL (1966). "The inhibition of mitochondrial peroxidation by ubiquinone and ubiquinol". The Journal of Biological Chemistry 241 (19): 4353–6. PMID 5922959. 
  2. ^ Mellors, A.; Tappel, A. L. (1966). "Quinones and quinols as inhibitors of lipid peroxidation". Lipids 1 (4): 282–4. doi:10.1007/BF02531617. PMID 17805631. 
  3. ^ Banerjee R (2007). Redox Biochemistry. John Wiley & Sons. p. 35. ISBN 978-0-470-17732-7. 
  4. ^ James, Andrew M.; Cochemé, Helena M.; Smith, Robin A. J.; Murphy, Michael P. (2005). "Interactions of Mitochondria-targeted and Untargeted Ubiquinones with the Mitochondrial Respiratory Chain and Reactive Oxygen Species: Implications for the use of exogenous ubiquinones as therapies and experimental tools". Journal of Biological Chemistry 280 (22): 21295–312. doi:10.1074/jbc.M501527200. PMID 15788391. 
  5. ^ Hosoe, Kazunori; Kitano, Mitsuaki; Kishida, Hideyuki; Kubo, Hiroshi; Fujii, Kenji; Kitahara, Mikio (2007). "Study on safety and bioavailability of ubiquinol (Kaneka QH™) after single and 4-week multiple oral administration to healthy volunteers". Regulatory Toxicology and Pharmacology 47 (1): 19–28. doi:10.1016/j.yrtph.2006.07.001. PMID 16919858. 
  6. ^ Judy, William. "Coenzyme Q10 Facts or Fiction". Thorne Research. Retrieved 9 December 2013. 
  7. ^ Kubo, Hiroshi; Fujii, Kenji; Kawabe, Taizo; Matsumoto, Shuka; Kishida, Hideyuki; Hosoe, Kazunori (2008). "Food content of ubiquinol-10 and ubiquinone-10 in the Japanese diet". Journal of Food Composition and Analysis 21 (3): 199–210. doi:10.1016/j.jfca.2007.10.003. 
  8. ^ Slater, E.C. (1983). "The Q cycle, an ubiquitous mechanism of electron transfer". Trends in Biochemical Sciences 8 (7): 239–42. doi:10.1016/0968-0004(83)90348-1. 
  9. ^ Trumpower BL (June 1990). "Cytochrome bc1 complexes of microorganisms". Microbiol. Rev. 54 (2): 101–29. PMC 372766. PMID 2163487. 
  10. ^ Trumpower, Bernard L. (1990). "The Protonmotive Q Cycle". The Journal of Biological Chemistry 265 (20): 11409–12. PMID 2164001. 
  11. ^ http://proteopedia.org/wiki/index.php/Complex_III_of_Electron_Transport_Chain[full citation needed][unreliable medical source?]

External links[edit]